When a moving member is stopped at a predetermined position, a buffer, in other words, a shock absorber is used for damping the kinetic energy of the moving member, and for reducing an impact force applied to the moving member. As one example, the shock absorber may have a double tube structure having an outer tube and an inner tube.
In a shock absorber of this type, a liquid accommodating chamber is provided in the inner tube, and liquid is injected into the liquid accommodating chamber. The liquid accommodating chamber is communicated with the space between the inner tube and the outer tube via communication holes provided in the inner tube. A piston is provided at a base end of a piston rod, and movable in the axial direction in the liquid accommodating chamber. When an impact force is applied to the piston rod from the moving member, and the piston is moved by the impact force so as to discharge liquid to the outside of the liquid accommodating chamber via the communication holes, the piston receives a flow resistance from the liquid, and the kinetic energy of the moving member is damped by the flow resistance. The damping amount is adjusted by changing the open degree of the communication holes so as to change the flow resistance of the liquid flowing through the communication holes.
Japanese Patent Publication No. S54-38270 discloses a hydraulic buffer having a cylinder, in other words, an inner tube in which a piston rod is built, and having a case body, in other words, an outer tube rotatably mounted on the outside face of the cylinder. An adjusting ring and an accumulator are attached to the case body, and the adjusting ring and the accumulator are disposed in a liquid chamber formed in a cylindrical shape between the cylinder and the case body. An orifice, in other words, the distance between the communication holes and the adjusting ring is changed by rotation of the adjusting ring so that the flow resistance of the liquid is changed.
Japanese Utility Model Publication No. S61-66235 discloses a buffer in which an inner cylinder and a floating piston are coaxial with and built in a cylinder. The inner cylinder is rotatably built in the cylinder, a projecting end thereof is projecting from a first end of the cylinder, and a piston rod is projecting from the projecting end of the inner cylinder. A fluid chamber formed between the inner cylinder and the floating piston is communicated with a liquid accommodating chamber in the inner cylinder through through-holes, and an eccentric V-shaped groove communicated with the through-holes are provided on the inner surface of the cylinder.
Japanese Utility Model Publication No. H06-28377 discloses a fluid-pressure buffer device having a metering tube and a pressure tube which is rotatably built in the metering tube. An eccentric groove is formed on the outer surface of the pressure tube, holes opened to the eccentric groove are formed in the pressure tube, and an orifice is provided on the metering tube. Therefore, the liquid in the pressure tube is flowed to the outside of the metering tube via the holes, the eccentric groove, and the orifice.
As described in Japanese Patent Publication No. S54-38270, in the hydraulic buffer configured so that the liquid chamber is formed in the cylindrical shape between the cylinder and the case body and that the adjusting ring and the accumulator are disposed in the liquid chamber, the outer diameter of the case body is large, and the buffer cannot be reduced in size. Moreover, in the structure in which the adjusting ring is configured to be attached to the case body by a ball-stop screw, attachment strength between the adjusting ring and the case body cannot be increased in a small buffer, and it is difficult to apply this to a small buffer.
As described in Japanese Utility Model Publication No. S61-66235, in a case where the inner cylinder and the floating piston are built in the cylinder, the buffer cannot be reduced in size. Moreover, the projecting end of the inner cylinder, which adjusts an aperture degree, has to be provided in the same side as the projecting end of the piston rod. More specifically, since an adjusting mechanism of the aperture degree is in the side in which a workpiece collides with the piston rod, the damping amount cannot be easily adjusted.
Furthermore, as described in Japanese Utility Model Publication No. H06-28377, in a case where the orifice is provided on the outside metering tube, a tube has to be further provided in the outside of the metering tube. Therefore, the buffer cannot be reduced in size.